1. Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular, to a method and apparatus for heating a nozzle.
2. Related Art
Conventional hot runner nozzles often have an uneven distribution of heat along the length thereof when operating in an injection molding apparatus. Uneven heat distributions in nozzles are undesirable because with the increased use of more difficult to mold plastic materials, the melt must be maintained within narrower and narrower temperature ranges. If the temperature rises too high, degradation of the melt will result, and if the temperature drops too low, the melt will clog in the system and produce an unacceptable product. Both extremes can necessitate the injection molding apparatus being shut down for a clean out, which is a very costly procedure due to the loss of production time.
Conventional hot runner nozzles are typically comprised of a nozzle body that is formed from a thermally conductive metal. The nozzle body is surrounded by a heating element that is either in contact with an outer surface of the nozzle or embedded therein. The melt channel, which extends through the nozzle, is heated by the conduction of heat from the heating element.
Conduction is sometimes an inefficient method of heating. Conduction methods of heating can result in a rapid loss of heat as one moves away from the heat source. Further, heat loss occurs at any point of contact between the heated nozzle and a lower temperature part of the injection molding apparatus.
There have been many attempts to reduce the amount of heat loss from the nozzle during the injection process. Conventional solutions have generally been directed toward minimizing the amount of contact between the nozzle and the surrounding mold plates or providing insulation at these contact points. Several of these solutions have reduced the amount of heat loss from the nozzle, however, the method of heating the nozzle has not changed significantly. Also, if precision heating of a certain area of a hot runner nozzle is desired, heat by conduction is difficult to precisely direct and thus ineffective in such applications.
Therefore, what is needed is a system and method that include using a heating device that heats a nozzle, which can provide “remote/projected” precision heating through directed radiation energy from a radiant energy source. What is also needed is a system and method that allows the nozzle length to be increased without requiring modification of the nozzle heater.